Those in the field of prosthetics have in the past manufactured prosthetic feet which permit varying degrees of motion capability. Most of the known prosthetic feet utilize metal hinges with rubber bumpers to enable this motion capability. These components are sources for mechanical failures and wear. The known prosthetic feet are also generally expensive to produce and maintain. None of the conventional prosthetic feet mimic human gait characteristics, e.g., while known designs allow some motion capability, the conventional prosthetic feet do not reflect humanoid characteristics. These characteristics relate to the biomechanical function of the human foot and ankle joint in gait. The prior art prosthetic feet have not achieved true human gait characteristics because their design features do not mimic the human foot.
The human foot is a complex comprised of twenty-six separate bones. The bones of the foot articulate with one another to create joints. The joints of the foot, through these articulations, allow movement to occur. The motion capability of a particular joint is dependent upon bony articulations, ligamentous reinforcements and muscular control. Motion capability of specific joints of the foot has been studied quite extensively through history. These scientific studies have identified fourteen different axes of rotations of all the joints of the human foot. They have through thoughtful analysis determined how these axes of rotations and motion capabilities function in human gait and running and jumping activities. The prosthetic foot of the present invention has been made in light of these scientific studies with a view toward providing an improved prosthetic foot that mimics the human foot in function in order to provide the amputee with normal human gait characteristics and improve the quality of life of the amputee.
A prosthetic foot according to the present invention comprises a forefoot portion, a midfoot portion and a hindfoot portion, wherein the hindfoot portion includes first and second joints permitting closed kinetic chain motion of the prosthetic foot in gait. The first joint has a joint axis oriented for permitting motion of the hindfoot portion about the first joint axis which is at least primarily in the sagittal plane. The second joint has a joint axis oriented for permitting motion of the hindfoot portion about the second joint axis which is at least primarily in the frontal and transverse planes. In the disclosed example embodiments, the first and second joints are formed integrally with the hindfoot portion by respective struts of resilient material of the hindfoot portion. More particularly, in one example embodiment the forefoot, midfoot and hindfoot portions of the prosthetic foot are formed of a single piece of plastic as by molding and/or machining.
In a second embodiment, the improved prosthetic foot of the invention is formed by use of an ankle pylon component of the invention which is attached to an existing low profile prosthetic foot as a functional upgrade. The ankle pylon component contains the first and second joints which form part of the hindfoot portion of the foot. In both embodiments, the first joint in the hindfoot portion mimics an ankle joint and the second joint mimics a subtalar joint to allow the foot to function like a normal foot.
The subtalar joint in the hindfoot portion of the disclosed embodiments constitutes a means for permitting triplanar closed kinetic chain motion of the prosthetic foot in gait. This triplanar motion capability improves the foot staying plantar grade during the stance phase of gait. It also decreases residual limb to socket shear forces associated with motion in the transverse plane.
These and other objects, features and advantages of the present invention will become more apparent from the following detailed description of the disclosed, example embodiments, taken with the accompanying drawings.